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February 20, 2018 Categories: Java Collections. No Comments on ArrayList in Java

Introduction to ArrayList

 

ArrayList class uses a dynamic array for storing a list of elements. It is inherited from AbstractList class and implements List interface. Following are some important points about ArrayList:

 

  • ArrayList can contain duplicate elements.
  • ArrayList size varies. When number of elements increase, size of ArrayList increases automatically, and when number of elements decrease, size of ArrayList also decreases.
  • ArrayList preserves the insertion order of elements.
  • ArrayList class is non-synchronized.
  • ArrayList allows random access of elements as it uses an array to store elements.
  • ArrayList is slow when insertion or deletion of elements is performed.

 

ArrayList Constructors

 

Following constructors are supported by the ArrayList class:

 

Constructor Description
ArrayList( ) Build an empty array list
ArrayList(Collection c) Builds an array list with the given collection c
ArrayList(int capacity) Builds an array list with specified initial capacity

 

ArrayList Methods

 

Following are some of the most frequently used methods of ArrayList:

 

Method Description
boolean add(Object o) Add the given element at the end of the list
void add(int index, Object element) Used to insert given element at the specified index in a list.
boolean addAll(Collection c) Add all the elements in the given collection c at the end of the list.
boolean addAll(int index, Collection c) Add the elements in the given collection at the end of the list.
void clear( ) Clear all the elements in the list and make it empty.
Object clone( ) Returns a shallow copy of the list
int indexOf(Object o) Returns the index of the given element on the list. Otherwise, returns -1 if the element is not present in the list.
int lastIndexOf(Object o) Returns the index of last occurrence of the given element in the list. Otherwise, returns -1 if the element is not present in the list.
Object[ ] toArray() Converts all the elements in the list to an array.
Object[ ] toArray(Object[ ] a) Converts all of the elements in this list in the correct order.

 

ArrayList Example

 

Following is an example program which demonstrates adding elements to a ArrayList and displaying them using a for  each loop:

 

 

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